As a physicist working on the Giant Hadron Collider (LHC) at Cern, some of the frequent questions I’m requested is “When are you going to search out one thing?” Resisting the temptation to sarcastically reply “Apart from the Higgs boson, which received the Nobel Prize, and an entire slew of recent composite particles?”, I notice that the rationale the query is posed so usually is all the way down to how we now have portrayed progress in particle physics to the broader world.
We frequently speak about progress by way of discovering new particles, and it usually is. Learning a brand new, very heavy particle helps us view underlying bodily processes – usually with out annoying background noise. That makes it straightforward to clarify the worth of the invention to the general public and politicians.
Not too long ago, nonetheless, a sequence of exact measurements of already recognized, bog-standard particles and processes have threatened to shake up physics. And with the LHC on the point of run at higher energy and intensity than ever earlier than, it’s time to begin discussing the implications broadly.
In fact, particle physics has all the time proceeded in two methods, of which new particles is one. The opposite is by making very exact measurements that check the predictions of theories and search for deviations from what is anticipated.
The early proof for Einstein’s concept of common relativity, for instance, got here from discovering small deviations within the obvious positions of stars and from the movement of Mercury in its orbit.
Three key findings
Particles obey a counter-intuitive however massively profitable concept known as quantum mechanics. This concept exhibits that particles far too large to be made instantly in a lab collision can nonetheless affect what different particles do (by one thing known as “quantum fluctuations”). Measurements of such results are very advanced, nonetheless, and far more durable to clarify to the general public.
However current outcomes hinting at unexplained new physics past the usual mannequin are of this second sort. Detailed studies from the LHCb experiment discovered {that a} particle generally known as a magnificence quark (quarks make up the protons and neutrons within the atomic nucleus) “decays” (falls aside) into an electron way more usually than right into a muon – the electron’s heavier, however in any other case similar, sibling. In accordance with the usual mannequin, this shouldn’t occur – hinting that new particles and even forces of nature might affect the method.
Intriguingly, although, measurements of comparable processes involving “prime quarks” from the ATLAS experiment on the LHC present this decay does happen at equal rates for electrons and muons.
In the meantime, the Muon g-2 experiment at Fermilab within the US has just lately made very precise studies of how muons “wobble” as their “spin” (a quantum property) interacts with surrounding magnetic fields. It discovered a small however vital deviation from some theoretical predictions – once more suggesting that unknown forces or particles could also be at work.
The latest surprising result is a measurement of the mass of a basic particle known as the W boson, which carries the weak nuclear pressure that governs radioactive decay. After a few years of information taking and evaluation, the experiment, additionally at Fermilab, suggests it’s considerably heavier than concept predicts – deviating by an quantity that might not occur by likelihood in additional than 1,000,000 experiments. Once more, it could be that but undiscovered particles are including to its mass.
Curiously, nonetheless, this additionally disagrees with some lower-precision measurements from the LHC (offered in this study and this one).
The decision
Whereas we aren’t completely sure these results require a novel rationalization, the proof appears to be rising that some new physics is required.
In fact, there shall be nearly as many new mechanisms proposed to clarify these observations as there are theorists. Many will look to numerous types of “supersymmetry”. That is the concept there are twice as many basic particles in the usual mannequin than we thought, with every particle having a “tremendous companion”. These might contain further Higgs bosons (related to the sphere that offers basic particles their mass).
Others will transcend this, invoking much less just lately trendy concepts equivalent to “technicolor”, which might suggest that there are further forces of nature (along with gravity, electromagnetism and the weak and powerful nuclear forces), and may imply that the Higgs boson is in actual fact a composite object fabricated from different particles. Solely experiments will reveal the reality of the matter – which is nice information for experimentalists.
The experimental groups behind the brand new findings are all properly revered and have labored on the issues for a very long time. That stated, it’s no disrespect to them to notice that these measurements are extraordinarily troublesome to make. What’s extra, predictions of the usual mannequin normally require calculations the place approximations need to be made. This implies totally different theorists can predict barely totally different lots and charges of decay relying on the assumptions and stage of approximation made. So, it could be that once we do extra correct calculations, among the new findings will match with the usual mannequin.
Equally, it could be the researchers are utilizing subtly totally different interpretations and so discovering inconsistent outcomes. Evaluating two experimental outcomes requires cautious checking that the identical stage of approximation has been utilized in each circumstances.
These are each examples of sources of “systematic uncertainty”, and whereas all involved do their greatest to quantify them, there might be unexpected issues that under- or overestimate them.
None of this makes the present outcomes any much less fascinating or essential. What the outcomes illustrate is that there are a number of pathways to a deeper understanding of the brand new physics, and so they all should be explored.
With the restart of the LHC, there are nonetheless prospects of recent particles being made by rarer processes or discovered hidden underneath backgrounds that we now have but to unearth.
This text by Roger Jones, Professor of Physics, Head of Division, Lancaster University is republished from The Conversation underneath a Inventive Commons license. Learn the original article.
